Method and apparatus for establishing a fixed support of a buoyant body in rough water



3,429,127 ESTABLISHING A FIXED su ODY IN ROUGH WATER PPORT Feb. 25, 1969J. M. DONKERS METHOD AND APPARATUS FOR OF A BUOYANT B Filed Feb. 11,1966 Fl 6. I

INVENTOR JACOBUS M. DONKERS ATTORNEYS.

6501996 US. Cl. 61-46.5 Int. Cl. E02!) 17/02 3 Claims ABSTRACT OF THEDISCLOSURE An offshore drilling rig is provided with extensiblesupporting legs and auxiliary buoyancy devices. The latter raise the rigabove its normal buoyancy level so that the legs may be extended andlocked whereafter the auxiliary buoyancy is suddenly terminated to setthe legs.

The invention relates to a method of carrying out operations on the bedof very rough water from a pontoon which is floated to its place ofdestination and which rests on the bed by means of extensible legsduring the operations. The object of the invention is to provide amethod of this kind wherein the time during which the pontoon can strikeagainst the bed is reduced to zero. To this end, according to theinvention, at the destination the bottom of the pontoon is firstadjusted to a level above the bed such as to correspond to the height ofthe expected irregularities of the bed plus the wave height, legs freelymovable vertically with respect to the pontoon are then brought intocontact with the bed, the legs are then secured against displacementwith respect to the pontoon and at the same time part of the pontoonbuoyancy is eliminated, water ballast is then taken in if necessary togive the required loading of the legs, and after conclusion of theoperations the various actions are carried out in the reverse sequence.By means of such a method, at the same time as the connection to thepontoon is effected the legs are subjected to such heavy loading in aninfinitely short time that they can no longer come free of the bed andhence a collision with the bed is impossible. The dan gerous transitiontime between the floating of the pontoon and the time when the samerests on the bed via the legs with an adequate loading is thus avoided.

According to the invention, before operations begin the simultaneoussecuring of the legs and elimination of part of the buoyancy and aftercompletion of the activities the reincorporation of the eliminatedbuoyance take place at the moment the pontoon is on a Wave crest. Theloading occurring as a result of elimination of part of the buoyancy isthen intensified by the Water level which is falling with respect to thepontoon. On re-incorporation of the buoyancy, there is no reversal ofthe direction of the forces when the water next falls. This givesmaximum stability for the floating pontoon.

According to the invention, that part of the pontoon which is requiredto provide the eliminated buoyancy during operations can be kept abovethe water level. This part of the pontoon cannot then exert horizontalforces on the pontoon as a result of the Water movement.

According to the invention, before operations are started the pontooncan be lowered with respect to the legs to an extent such that thatportion of the pontoon which is required to provide the remainingbuoyancy is as far as possible outside the influence of the wave motion.The loading of hte pontoon in the horizontal direction during 3,429,127Patented Feb. 25, 1969 the performance of the Operations is also reducedas a result.

The invention also relates to a pontoon for performing one or more ofthe above-described methods, such a pontoon having extensible legsmovable freely with respect to the pontoon and adapted to be securedagainst displacement with respect to the pontoon.

To this end, according to the invention, a number of the floats of thepontoon are vertically movable with respect to the pontoon and can besecured against displacement in any required position with respect tothe pontoon. A considerable loading on the pontoon legs can be obtainedin an infinitely short time by suddenly eliminating the security ofthese movable floats against displacement.

In one advantageous embodiment of the pontoon according to theinvention, the movable floats are each secured to the free end of an armpivotally connected to the outside of the pontoon, said arm beingadapted to swing in a vertical plane and lockable at a given angle withrespect to the pontoon by means of cables secured to said arm any bymeans of a Winch disposed on the pontoon. A construction of this kindfor the pontoon gives maximum stability while the movable floats are inoperation, while when they are in-operative they can be brought as closeto the pontoon as possible so as to provide the minimum obstruction.

The invention will be explained in detail in the following descriptionof one exemplified embodiment of a pontoon according to the inventionwith reference to the accompanying drawing, wherein:

FIG. 1 is an end view of a pontoon according to the invention.

FIG. 2 is a top plan view of a pontoon shown in FIG. 1.

The pontoon consists of a rectangular box-shaped frame-work 1 having afree opening 2 which can be covered by grids to form a work floor. Oneor more travelling bridge structures 3 are provided on the frame workand each bears a drilling derrick 4 adapted to travel over the bridgestructure. By means of posts 5 the framework '1 rests on longitudinallyextending cylindrical floats 6.

These cylinders can also accommodate water ballast and they also containchambers for the storage of oil and drinking water, pump chambers alsobeing provided in said floats.

Extending legs 7 with the associated actuating mechanisms are providedin the posts 5 which are disposed at the corners of the framework. Thelegs 7 are actuated by hydraulic cylinders. They can be locked in anyrequired position with respect to the posts 5 and can also be connectedto a compensation system (not shown) to enable the legs 7 to rest on thesea bed, while the framework 1 can move freely up and down along thelegs 7 via the posts 5 under the influence of the rise and fall of the'Water.

Laterally of the pontoon, arms 9 in the form of triangular frameworksare secured by hinges at 8 to pairs of the posts 5 and they carriedvertically movable floats 10. A winch 11 is provided on the pontoon foreach float 10 and comprises two drums 12 and 13, one of which has acable 15 running over it to the end of the arm 9 via pulley 14. From theother drum a cable 18 extends to the free end of the arm 9 via a pulley16 and a pulley 17, the latter being secured to a float 6. The float 10can be hoisted to position 10 by means of cable 15. The buoyancyprovided by the float 10 can be transmitted to the pontoon by means ofthe cable 18, which may comprise a plurality of parts. Since the floats10 are situated at a relatively considerable distance outside theboxshaped framework 1, the floats 10 contribute very considerably to thestability of the floating pontoon.

The winch 11 also comprises a drum 19 on which a cable 20 can be wound,by means of lwhich the pontoon can be anchored at the four corners.

When it is required to place the pontoon on the bed 21 the procedure isas follows. The pontoon is first anchored at the required place by meansof cables 20 and then the pontoon draught is so adjusted by pumpingwater ballast into the floats 6 that the bottom of the latter is at adistance from the bed 21 equal to the expected irregularities of the bed21 plus the wave height in order to assure that the floats 6 do notstrike the bed when the pontoon is in the trough between waves, thecables 15 and 18 being used to adjust the floats 10 so that they aresubstantially half submerged. The legs 7 are then dropped until theyrest on the bed 21 while still being freely movable with respect to theposts 5. At this point, the floats 10 are substantially half submergedwhile the buoyancy of the entire structure is such as to place thefloats 6 in such a position that they are in proximity to the bed 21 butcannot strike it when the trough between waves is encountered.

When the pontoon is at the crest of a wave, the legs 7 are securedagainst displacement with respect to the posts 5 and at the same timethe cable 18 is released. A great part of the weight of the pontoon thuscomes to rest on the legs 7 in one operation. The legs cannot thereforehave any pushing action on the bed. The floats are then raised toposition 10' by means of the cables 15. Water ballast is also admittedto the floats 6 to increase the loading of the legs 7 whenevernecessary. The pontoon can also be lowered along the legs 7 so that thefloats 6 are removed from the influence of the wave motion.

When it is required to release the pontoon from the bed after operation,the original distance between the bottom of the floats 6 and the bed 21is restored. The water ballast is then reduced until the pontoon is justnot floating on a wave crest. The floats 10 are then lowered and cable18 is payed out until the floats: 10 can follow the wave motion. Afterthe winch drums have been locked the legs 7 are freed and the floats 10are adjusted by means of the cables and 18 so that they are halfsubmerged. The legs 7 can then be drawn up and the required pontoondraught can be obtained by pumping out water ballast.

What I claim is:

1. A method of carrying out operations on the bed of very rough waterfrom a pontoon which is floated to its place of destination and whichrests on the bed by means of extensible legs during the operations,which method comprises adjusting the buoyancy of the pontoon so that thebottom of the pontoon is first adjusted to a level above the bed such asto correspond to the height of the expected irregularities of the bedplus the Wave height, contacting legs with the bed while maintainingsuch legs freely movable vertically with respect to the pontoon, andthen simultaneously securing said legs against displacement with respectto the pontoon and at the same time eliminating part of the pontoonbuoyancy.

2. A pontoon assembly adapted to be floated to a desired location on abody of Water and then supported on the bed of the body of watercomprising, in combination,

a pontoon,

buoyant means pivotally attached to said pontoon,

motion transmitting means for forcing said buoyant means downwardly inthe body of water to increase the buoyancy of the assembly,

a plurality of legs for supporting said pontoon on the bed, said legsincluding extensible portions so that the legs are, in eflect, rigiddepending extensions from said pontoon,

means for releasing said motion transmitting means suddenly to decreasethe buoyancy of the assembly, and

means for locking said extensible portions of the legs in engagementwith the bed.

3. A pontoon according to claim 2 wherein said buoyant means are in theform of floats, each secured to the free end of an arm pivotallyconnected to the outside of the pontoon, each arm being adapted to swingin a vertical plane and lockable at a given angle with respect to thepontoon by means of cables secured to said arm and by means of a winchdisposed on the pontoon.

References Cited UNITED STATES PATENTS 2,525,955 10/1950 Scott 6l--46.52,846,851 8/1958 Pelhan'i 6l46.5 2,895,300 7/1959 Hayward 6l46.52,938,352 5/1960 Knapp et a1. 6l-46.5 3,118,283 1/1964 True et al 6146.53,289,419 12/1966 McGowen 6146.S

JACOB SHAPIRO, Primary Examiner.

